Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image forming apparatus uses a color conversion table to convert input color values into output color values. A color conversion table for a primary color is constituted of a gamma correction table for each color material such as toner or ink, which is used for printing by an image forming apparatus. A color conversion table for a secondary (or more) color is formed based on gamma correction tables for a plurality of color materials.
Holding input-output characteristics of a primary color in each color material in accordance with a defined value holds colors reproduced by an image forming apparatus in constant state. However, input-output characteristics of a primary color changes due to, for example, a secular change. Thus, there is known a technique that adjusts input-output characteristics of a primary color to approach the defined value, by correcting the gamma correction table.
However, adjusting input-output characteristics of a primary color does not mean adjusting a balance of a whole region of an output color space. Consequently, even when input-output characteristics of a primary color is adjusted, in the case of a color of a secondary (or more) color, the color after having undergone a color conversion table sometimes has a problem of a collapsed balance of a plurality of primary colors, which constitute this color. This sometimes results in that the color does not necessarily match the defined color value and has a significant difference from a color in user's recognition.
Thus, as a method that reduces a difference between a color in user's recognition and an actually printed color, there is known an adjustment method that considers a whole region of a color space.
There is proposed an adjustment method that individually corrects each of a primary color and a secondary color. Then, the method obtains a correction value to correct a whole, by combining correction values obtained during correction.
There is also proposed an adjustment method that corrects a primary color and then sequentially corrects a secondary color and a tertiary color. The method attaches a weight to the primary color based on the obtained values.